1. Field of the Invention
The present invention relates to noninvasive diagnostic medical devices which utilize ultrasound to determine the heading and the speed of blood flowing in a blood vessel or in the heart.
2. Prior Art
The measurement of blood velocity using Doppler shifted ultrasonic echoes has proven clinically useful for the diagnosis of arterial and venous disorders since it's discovery by Koneko and Satamura in Osaka in 1957 (S. Satamura) and by Franklin and Baker in Seattle in 1959 (D. L. Franklin). Blood velocities in depressed, normal and elevated ranges (2 cm/s to 400 cm/s) interact with the wave speed of ultrasound in blood (157,000 cm/s) to create a Doppler frequency shift (0.0025% to 0.5%) in the ultrasound frequency. If the ultrasound frequency is selected for the strongest echoes from blood through the skin (1.5 MHz to 10 MHz), the Doppler frequency is within the normal hearing range of humans (20 Hz to 15,000 Hz) permitting the resultant Doppler signals to be heard. ##EQU1##
__________________________________________________________________________ Depth of Artery AUDIBLE DOPPLER FREQUENCIES Ultrasound Frequency FOR MUSCLE OVERLYING ARTERY Blood Doppler 10 cm 4 cm 2 cm Velocity Shift 1.5 MHz 5 MHz 10 MHz __________________________________________________________________________ 2 cm/s Depressed 0.0025% 38 Hz 127 Hz 255 Hz 100 cm/s Normal 0.125% 1910 Hz 6370 Hz 12,738 Hz 400 cm/s Elevated 0.5% 7643 Hz ##STR1## ##STR2## ##STR3## __________________________________________________________________________
The application of ultrasound to blood flowing in arteries is discussed below in connection with diagrams in the drawings illustrating blood flow phenomena in arteries.